The goals of Project 1 are to examine Tim1 and Tim3 as novel asthma susceptibility genes in man, and as T cell genes that regulate the differentiation of CD4 lymphocytes. We recently positionally cloned the Tim gene family, using a unique approach with congenic mice that simplified a complex genetic trait (asthma) into a simple Mendelian trait. The human homologues of the Tim genes lie on chromosome 5q33.2, a region repeatedly linked to asthma. Moreover, the human homologue of Tim1 encodes the cellular receptor for the hepatitis A virus (HAV), suggesting that CD4 T cells and TIM-1 may mediate the known protective effect of prior infection with HAV on the development of atopy. Since the prevalence of HAV infection is greatly reduced in industrialized countries, our findings may explain in part the enormous increase in asthma prevalence occurring over the past two decades, and strongly suggest that Tim1 plays a major role in directly regulating the development of human asthma and allergy. To determine if Tim gene polymorphisms are associated with the development of atopy, we will first identify coding region polymorphisms in, and the alleles of, human Tim1 and Tim3 by sequencing mRNA from activated T cells of 40 individuals. We will then determine whether Tim1 and Tim3 gene polymorphisms are associated with the development of atopy in 100 well characterized atopic and 100 nonatopic individuals. Subgroup analysis will also be performed examining the association of Tim gene polylmorphisms with asthma, allergy, specific IgE, and total IgE separately. Preliminary data indicate that the human Tim1 gene is highly polymorphic as it is in mice with significant coding region polymorphisms including amino acid deletions, and that Tim1 is indeed associated with elevated IgE and atopy. We will also analyze the cellular and molecular processes that occur when HAV binds to TIM-1 expressed on T lymphocytes. We will determine whether HAV alters the differentiation of CD4 T cells, reduces IL-4 production, proliferation, or enhances apoptosis. We will also determine if distinct polymorphisms of Tim1 affect binding affinity to HAV susceptibility of T cells to HAV infection, T cell differentiation and cytokine production. These studies of Tim genes, which are located on chromosome 5q33.2 and which we identified using a unique congenic mouse approach, will characterize an important human asthma susceptibility gene, and provide extraordinary insight into the immunologic, genetic and environmental pathways involved in the pathogenesis of asthma.